Golf ball

ABSTRACT

Disclosed herein is a golf ball which has not only an air resistance similar to or smaller than that of a dimpled golf ball, but also a significantly reduced area ratio of grooves relative to the total surface area of the golf ball, thereby achieving an enhanced carry distance and high accuracy in the directionality of putting. The golf ball has net-shaped grooves formed on an outer surface of a sphere.

TECHNICAL FIELD

The present invention is related to a golf ball, and more particularly,to a golf ball which has not only an air resistance similar to orsmaller than that of a dimpled golf ball, but also a significantlyreduced area ratio of grooves relative to the total surface area of thegolf ball, thereby achieving an enhanced carry distance and highaccuracy in the directionality of putting.

BACKGROUND ART

In general, a golf ball, which has a spherical surface divided into manyspherical polygonal faces each being arranged with a circular dimple,has been used for a long time. Such a conventional dimpled golf ball isknown to fulfill the symmetry of a spherical surface while achieving areduced air resistance and consequently an increased carry distancethereof.

Currently, examples of widely used divisional compositions of a sphereinclude a spherical icosahedron, a spherical icosi-dodecahedron, aspherical dodecahedron, a spherical octahedron, a spherical hexahedron,a spherical hexa-octahedron, or other further divided sphericalpolyhedrons having smaller faces. In golf balls having the same size asone another, the above mentioned spherical divisional compositions canbe actually overlapped with one another except for specially deformedones. Therefore, it can be concluded in a broad sense that the abovementioned spherical divisional compositions are identical to oneanother. If circular dimples of a golf ball are arranged on one of theabove divisional compositions, it can be said that a carry distance ofthe golf ball is determined by the area ratio of the dimples relative tothe total surface area of the golf ball.

If a golfer hits a dimpled golf ball, the dimpled golf ball is subjectedto strong repulsive elasticity by a force applied from the head of agolf club, and simultaneously has a back spin by a loft angle of theclub head. In the case where the golf club is a driver, for example, thedimpled golf ball has an initial flying velocity of approximately 190 to300 km/hr and an initial back spin of approximately 2200 to 4500 rpm. Inthis case, dimples of the golf ball act to create a turbulent flow onthe surface of the golf ball and in turn, the turbulent flow acts todelay the separation of air streams around the golf ball, therebyreducing a pressure difference between front and rear portions of thedimpled golf ball, and resulting in a reduction of air resistance actingon the golf ball.

Although there is a known hypothesis related to a dimpled golf ball, inthat air generates eddies inside dimples to thereby create a turbulentflow around a golf ball, the inventors of the present invention provedthrough an experiment that a turbulent flow around the golf ball iscreated through the shear layer instability as air separates at thedimple rather than entering into the dimple, as published in aprofessional journal “Physics of Fluids”(April, 2006).

DISCLOSURE OF INVENTION Technical Problem

However, to reduce an air resistance acting on a dimpled golf ball,generally, the area ratio of dimples relative to the total surface areaof the golf ball has to be more than 75%. This makes it impossible toachieve a high accuracy in the directionality of putting.

As shown in FIGS. 1 and 2, in a conventional dimpled golf ball 1 inwhich dimples occupy a great area ratio, a putter 2 generally strikesirregular faces formed with the dimples of the dimpled golf ball 1 andthis makes the golf ball 1 to move in a direction slightly differentfrom the golfer's intension. In other words, the golf ball deviates froma hole cup even by an extremely small angular error occurred in putting.

Technical Solution

Therefore, the present invention has been made in view of the aboveproblems, and the objective of the present invention is to provide agolf ball which has not only an air resistance similar to or smallerthan that of a dimpled golf ball by virtue of net-shaped grooves formedin a spherical surface thereof, but also a significantly reduced arearatio of the grooves relative to the total surface area of the golfball, thereby achieving an enhanced carry distance and high accuracy inthe directionality of putting.

Advantageous Effects

According to the present invention, a golf ball has net-shaped groovesformed throughout a sphere. With this configuration, an air resistanceacting on the golf ball is similar to or smaller than that acting on adimpled golf ball, thus resulting in an improvement in the carrydistance of the golf ball.

Further, according to the present invention, as a result of considerablyreducing the area ratio of the grooves relative to the surface area ofthe golf ball, it is possible to reduce the occurrence of putting errorsdue to the curvature of the grooves, resulting in accurate putting ofthe golf ball.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objective, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view illustrating a dimpled golf ball in aputting position;

FIG. 2 is a sectional view taken along the line A-A of FIG. 1;

FIG. 3 is a plan view illustrating a golf ball formed with groovesaccording to an embodiment of the present invention;

FIG. 4 is a schematic diagram of the grooves according to one embodimentof the present invention;

FIG. 5 is a schematic diagram of the grooves according to anotherembodiment of the present invention;

FIG. 6 is a schematic diagram of the grooves according to yet anotherembodiment of the present invention;

FIG. 7 is a photograph illustrating laboratory equipment having a modelof a golf ball according to the present invention;

FIG. 8 is a schematic diagram illustrating grooves formed in the surfaceof the model of the golf ball according to the present invention;

FIG. 9 is a photograph illustrating a model of a golf ball according tothe present invention, which has grooves and protrusions formed atintervals along the grooves;

FIGS. 10 and 13 are graphs illustrating the relationship between theReynolds number and the air resistance coefficient;

FIGS. 11 and 14 are graphs illustrating the relationship between thevelocity of a golf ball and the air resistance;

FIG. 12 is a photograph illustrating another model of a golf ballaccording to the present invention, which has grooves and protrusionscontinuously formed along the grooves; and

FIG. 15 is a partial sectional view of a golf ball having grooves andprotrusions formed along the grooves according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

To accomplish the above objective, the present invention provides a golfball in which net-shaped grooves are formed on the outer surface of asphere.

Now, preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. However, a detaileddescription related to known configurations or functions will be omittedif it is determined to make the subject matter of the present inventionunclear.

As shown in FIG. 3, the golf ball in accordance with a preferredembodiment of the present invention includes net-shaped grooves 20formed on the outer surface of a sphere 10. The net-shaped grooves 20may be connected to or separated from one another.

The shape of each groove 20 can be freely selected among a variety ofdifferent shapes so long as all the grooves 20 have a net shape. In oneembodiment of the present invention for forming the net-shaped grooves20, as shown in FIG. 4, first, a spherical regular polyhedron isinscribed in the sphere 10 such that vertexes 31 of spherical regularpolygons constituting the spherical regular polyhedron touch on thesphere 10. Then, certain specific points 33 a on a spherical surface ofthe sphere 10 are determined such that an included angle θ between astraight line 32 connecting one of the vertexes 31 to a center 11 of thesphere 10 and a straight line 34 connecting the center 11 of the sphere10 to one of the specific points 33 a has a predetermined value. Whenthe specific points 33 a are determined, circular paths 35 are definedon the surface of the sphere 10 by connecting the specific points 33 ato one another. The grooves 20 can be formed along the circular paths35. Here, each edge of the regular polyhedron is defined by connectingevery two adjacent vertexes 31 to each other via the shortest path onthe surface of the sphere 10.

The spherical regular polyhedron may be a spherical regular hexahedronor regular icosahedron, and the included angle θ may be 45 to 80degrees. The spherical regular hexahedron has six spherical squares andeight vertexes 31, and the spherical regular icosahedron has twentyspherical regular triangles and twelve vertexes 31. Therefore, when eachgroove is formed along one associated circular path 35 defined abouteach vertex 31 and consequently, eight or twelve grooves are formed inthe surface of the sphere 10 such that they are connected to oneanother, all the grooves 20 occupy only a small area ratio relative tothe surface area of the golf ball. This assists in putting of the golfball in a desired accurate direction. Assuming that a vertex 31 is thestagnation point and the sphere 10 has a smooth surface, separation ofair streams occurs at the angle θ of approximately 80 degrees.Accordingly, when eddies are generated by use of the grooves 20 beforethe separation occurs, the separation point is shifted to the angle θ of120 degrees. This can greatly reduce an air resistance acting on thegolf ball. In conclusion, it is preferable that the groove be formed onthe basis of the included angle θ of 45 to 80 degrees.

In another embodiment of the present invention as shown in FIG. 5, aspherical regular polyhedron, which consists of spherical regularpolygons each having a center of gravity 36, is inscribed in the sphere10, and specific points 33 b on the surface of the sphere 10 aredetermined such that an included angle θ between a straight line 37connecting one of the centers of gravity 36 to the center 11 of thesphere 10 and a straight line 38 connecting the center 11 of the sphere10 to one of the specific points 33 b has a predetermined value. If thespecific points 33 b are determined, circular paths 39 connecting thespecific points 33 b to one another are defined on the surface of thesphere 10. The grooves 20 can be formed along the circular paths 39.

Preferably, the spherical regular polyhedron is a spherical regularoctahedron or regular dodecahedron, and the included angle θ is 45 to 80degrees. The spherical regular octahedron has eight spherical regulartriangles and six vertexes 31, and the spherical regular dodecahedronhas twelve spherical regular pentagons and twenty vertexes 31.Therefore, when each groove is formed about each vertex 31 andconsequentially, six or twenty grooves are formed along the circularpaths 39 such that they are connected to one another. In this case,however, there is a problem in that the area ratio of the groovesrelative to the surface area of the golf ball may be too small to reducean air resistance acting on the golf ball down to a desired level, ormay be too large to improve the directionality of putting.

The shape of each groove can be changed into a variety of differentshapes other than the above described shapes, so long as all the groovesmaintain a net shape and fulfill the symmetry of a spherical surface,and the surface area of the grooves occupies 14 to 69% of the surfacearea of the golf ball.

In yet another embodiment of the present invention showing anotherdifferent shape of the grooves, the sphere 10 has a divisionalcomposition of a spherical polyhedron, and grooves are formed alongedges 41 of the spherical polyhedron. The spherical polyhedron may be aspherical regular icosahedron, or may be a spherical icosahedronconsisting of eight spherical regular pentagons and twelve sphericalregular hexagons as shown in FIG. 6. Even in the case where the outersurface of the sphere 10 is divided into spherical polygons fulfillingthe symmetry of a spherical surface for arrangement of dimples, thepresent invention is applicable in such a manner that grooves are formedalong the edges 41 of the spherical polyhedron. The grooves, formedalong the edges 41 of the spherical polyhedron, may be connected to orseparated from one another.

Referring to FIG. 7 illustrating laboratory equipment used in anexperiment of the present invention, an experimental model of a golfball was installed in a wind tunnel, to measure an air resistance actingon the experimental model while increasing the velocity of wind from 5m/s to 30 m/s by 1 m/s. On the basis of dimensional analysis andsimilarity, if a golf ball has the same Reynolds number as that of theexperimental model, the golf ball and the experimental model also havethe same air resistance coefficient as each other. Accordingly, an airresistance actually acting on the golf ball could be calculated based onexperimental values.

A method for forming grooves in the surface of the model used in theabove experiment will now be described in detail with reference to FIG.8. First, a regular hexahedron is inscribed in the model such that themodel has a divisional composition of a spherical regular hexahedron.Then, a circular path 35 a is defined about one vertex 31 a of aspherical square constituting the spherical regular hexahedron byconnecting three vertexes (only two vertexes 31 b and 31 c are visiblefrom FIG. 8) closest to the vertex 31 a to one another. In this case,the included angle θ is approximately 70 degrees. In the case of theremaining vertexes 31 b, 31 c, 31 d, . . . , similarly, circular paths35 b to 35 h thereof can be defined, and grooves can be formed along allthe circular paths 35 a to 35 h. When the outer surface of the sphere 10is divided, by the circular paths 35 a to 35 h, into a plurality ofcells, grooves can be additionally formed along shorter diagonal lines42 a, 42 b, 42 c, 42 d, . . . of some cells containing the edges 41 ofthe spherical regular hexahedron.

Considering now the detailed conditions of the above experiment, thediameter of the model was 150 mm. In Example 1, the outer surface of themodel was formed with grooves having a width of 5 mm and a depth of 0.5mm. In Example 2, protrusions having a height of 0.5 mm wereadditionally formed in the grooves. In Example 3, the protrusions werepartially cut and removed at intervals as shown in FIG. 9.

TABLE 1 Sphere's Groove's Groove's Protrusion's Diameter Width DepthHeight Example 1 42.67 mm 1.42 mm 0.142 mm Example 2 42.67 mm 1.42 mm0.142 mm 0.142 mm Example 3 42.67 mm 1.42 mm 0.142 mm 0.142 mm

Values in Table 1 represent reduced values of the models and should beconsidered as actual numerical values of the golf ball having groovesformed in the surface thereof on the basis of dimensional analysis andsimilarity.

FIG. 10 is a graph illustrating the relationship between the Reynoldsnumber and the air resistance coefficient, and FIG. 11 is a graphillustrating the relationship between the velocity of a golf ball andthe air resistance. These graphs are for the comparison of an airresistance acting on the grooved golf ball of the present invention withthat acting on a conventional dimpled golf ball.

In the case of Example 1, an air resistance acting on the grooved golfball begins to be smaller than that acting on the dimpled golf ball fromthe critical point where the Reynolds number is approximately 190,000(the velocity of the golf ball is 240 km/hr). Since the initial velocityof a drive shot is 190 to 300 km/hr, the overall air resistance actingon the grooved golf ball is larger than that acting on the dimpled golfball, thus suffering from a reduction of a carry distance andconsequently, being unsuitable for use as a golf ball. In conclusion,when the width of the grooves is smaller than 2 mm and no protrusionsare formed in the grooves, the air resistance acting on the grooved golfball exceeds that acting on the dimpled golf ball, resulting in areduced carry distance of the golf ball. Therefore, in this case, it ispreferable that the number of the grooves, having the width of 2 mm orless, be increased as compared to that of Example 1, so as to increasethe area ratio of the grooves relative to the surface area of the golfball, for the sake of reducing the air resistance acting on the golfball.

In Example 2 in which protrusions are formed in the grooves, it is seenfrom FIGS. 10 and 11 that the air resistance acting on the grooved golfball is smaller than that acting on the dimpled golf ball except for aregion where the Reynolds number is 50,000(80 km/hr) to 110,000(140km/hr). As compared to the dimpled golf ball in which the area ratio ofdimples relative to the surface area of the dimpled golf ball isapproximately 75 to 84%, the area ratio of the grooves relative to thesurface area of the grooved golf ball is only approximately 23%.Therefore, the grooved golf ball of Example 2 could achieve a remarkablereduction in the occurrence of putting errors due to the curvature ofthe grooves, thus enabling accurate putting of the golf ball.

Example 3 has the same experimental conditions as those of Example 2except for the fact that the protrusions formed in the grooves arepartially cut and removed at intervals, rather than being continuouslyconnected to one another. Similar to Example 2, the air resistanceacting on the golf ball of Example 3 is smaller than that acting on thedimpled golf ball.

In the experiment of the present invention, also, other models having adiameter of 150 mm are considered. In Example 4, the outer surface ofthe model is formed with grooves having a width of 10 mm and a depth of1 mm. In Example 5, continuous protrusions having a height of 1 mm areformed in the grooves as shown in FIG. 12.

TABLE 2 Sphere's Groove's Groove's Protrusion's Diameter Width DepthHeight Example 4 42.67 mm 2.84 mm 0.284 mm Example 5 42.67 mm 2.84 mm0.284 mm 0.284 mm

Values in Table 2 represent reduced values of the models and should beconsidered as actual numerical values of the golf ball having groovesformed in the surface thereof on the basis of dimensional analysis andsimilarity.

FIG. 13 is a graph illustrating the relationship between the Reynoldsnumber and the air resistance coefficient, and FIG. 14 is a graphillustrating the relationship between the velocity of a golf ball andthe air resistance. These graphs are for the comparison of an airresistance acting on the grooved golf ball of the present invention withthat acting on a conventional dimpled golf ball.

Although Examples 4 and 5 show the air resistances acting on the groovedgolf ball similar to that acting on the dimpled golf ball, it could beappreciated that the area ratios of grooves relative to the surface areaof the respective golf balls of Examples 4 and 5 are only approximately46%, thereby enabling accurate putting of the golf ball as compared tothe dimpled golf ball.

When no protrusions are formed in the grooves, it is preferable that thegroove 20 have a width W below 4 mm and a depth GH of 0.1 to 0.4 mm inconsideration of the air resistance acting on the golf ball and theaccurate directionality of putting. If the depth GH of the groove 20 issmaller than 0.1 mm, RPM of the backspin of the grooved golf balldecreases as compared to that of the dimpled golf ball, thus resultingin a reduced lift force.

As shown in FIG. 15, when a protrusion 21 is formed in the groove 20,the width W of the groove 20 is preferably 1 to 5 mm, and the depth GHof the groove 20 is preferably 0.1 to 0.5 mm. Also, in consideration ofthe accurate directionality of putting, the height H of the protrusion21 is preferably smaller than the depth GH of the groove 20. Similar tothe grooves 20, the protrusion 21 may be connected to or separated fromother protrusions.

Here, it can be appreciated that the width W and the depth GH of thegroove 20 and the height H of the protrusion 21, formed in the surfaceof the sphere 10, may be changed per their locations such that a varietyof different sizes of grooves 20 or protrusions 21 exist together in thesingle sphere 10.

INDUSTRIAL APPLICABILITY

As apparent from the above description, according to the presentinvention, a golf ball has net-shaped grooves formed throughout asphere. With this configuration, an air resistance acting on the golfball is similar to or smaller than that acting on a dimpled golf ball,thus resulting in an improvement in the carry distance of the golf ball.

Further, according to the present invention, as a result of considerablyreducing the area ratio of the grooves relative to the surface area ofthe golf ball, it is possible to reduce the occurrence of putting errorsdue to the curvature of the grooves, resulting in accurate putting ofthe golf ball.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A golf ball wherein net-shaped grooves are formed on an outer surfaceof a sphere, and the net-shaped grooves are connected to or separatedfrom one another.
 2. The golf ball according to claim 1, wherein thearea of the grooves is 14 to 69% of the total surface area of the golfball.
 3. The golf ball according to claim 2, wherein each groove has awidth below 4 mm and a depth of 0.1 to 0.4 mm.
 4. The golf ballaccording to claim 2, wherein each groove has a width of 1 to 5 mm and adepth of 0.1 to 0.5 mm, and the groove is formed with a protrusionmerely having a height smaller than the depth of the groove, and theprotrusion is connected to or separated from other protrusions.
 5. Thegolf ball according to claim 1, wherein the sphere has a divisionalcomposition of a spherical regular polyhedron, and each groove is formedalong a circular path drawn by connecting specific points on the surfaceof the sphere, each specific point being determined such that anincluded angle between a straight line connecting one of vertexes ofspherical regular polygons constituting the spherical regular polyhedronto a center of the sphere and a straight line connecting the specificpoint to the center of the sphere has a predetermined value.
 6. The golfball according to claim 5, wherein the spherical regular polyhedron is aspherical regular hexahedron or regular icosahedron, and the includedangle is 45 to 80 degrees.
 7. The golf ball according to claim 1,wherein the sphere has a divisional composition of a spherical regularpolyhedron, and each groove is formed along a circular path drawn byconnecting specific points on the surface of the sphere, each specificpoint being determined such that an included angle between a straightline connecting one of centers of gravity of spherical regular polygonsconstituting the spherical regular polyhedron to a center of the sphereand a straight line connecting the specific point to the center of thesphere has a predetermined value.
 8. The golf ball according to claim 7,wherein the spherical regular polyhedron is a spherical regularoctahedron or regular dodecahedron, and the included angle is 45 to 80degrees.
 9. The golf ball according to claim 1, wherein the sphere has adivisional composition of a spherical polyhedron, and the grooves areformed along edges of the spherical polyhedron.
 10. The golf ballaccording to claim 9, wherein the spherical polyhedron is a sphericalregular icosahedron, or a spherical icosahedron consisting of eightspherical regular pentagons and twelve spherical regular hexagons.